Wehavedevelopedanewapproachtotheconstructionofmolecular mechanics force fields, motivated by previous work in which existing force fields were shown to have major deficiencies, for example in prediction free energies of amine and amide solvation. We have shown that a simple electrostatic polarizable model can accurately reproduce the many-body part of the quantum mechanical energy of a molecular cluster (e.g. water trimer) if the model is fit to the quantum chemical polarization response, a straightforward procedure. Two polarizable models, the fluctuating charge model of Berne and coworkers and the polarizable dipole model of Levy and coworkers, are being investigated. The final potential function can then be constructed by adding a pair potential to fit the gas phase dimer energies of a molecular pair. Preliminary results have been obtained for water which yield a reasonable result for liquid phase simulations without any fitting of the parameters to condensed phase data. A. Scientific Subproject